It is well known that the ability of a lubricating oil to protect moving parts from wear can be markedly enhanced by the addition of small concentrations of certain additives, notably those containing sulfur. Probably the most common employed antiwear additives are the zinc dialkyl and diaryl dithiophoshates, which are used in most automobile crankcase oils and in numerous other lubricants and hydraulic fluids. However, sulfur-containing antiwear additives are not always satisfactory in lubricant formulations which must withstand operating temperatures in excess of 300.degree.F., such as some of the modern gas turbine lubricants. At these temperatures, especially in the presence of air, the zinc dithiophosphates and most of the other sulfur-containing antiwear agents decompose into products which are highly corrosive to copper and other common bearing materials. Furthermore, for many applications, ashless formulations -- that is, formulations which leave no residue on evaporation or combustion -- are preferred; and, of course, metal-containing antiwear agents like the zinc dithiophosphates are not suitable for such products.
One ashless antiwear agent that does not contain sulfur and is stable and noncorrosive at temperatures above 300.degree.F. is tricresyl phosphate, familiarly known as "TCP." Tricresyl phosphate is used in many lubricant products wherein the use of zinc dithiophosphates or other sulfur-containing antiwear additives is undesirable for one or more of the reasons given hereinabove. However, as an antiwear additive, TCP is not as effective as many of the sulfur-containing additives; and, thus, there is a need for an ashless antiwear agent with the high temperature capabilities of TCP but with improved antiwear properties.